Missing root VG, dropped to an initramfs shell

Make sure your "/boot/grub/grub.cfg" lists the correct VG and LV. In my case, the VG is named "ssd_vg" and the LV is named "root_lv", so the grub.cfg file needs to reference "/dev/mapper/ssd_vg-root_lv" (note use of slashes and dashes!).